1. Field of the Invention
The present invention relates generally to the field of wireless telemetry and, more specifically, to a system and method for simplifying the creation of a direct sequence spread spectrum (DSSS) radio transmitter. The invention taught herein greatly simplifies the required hardware and software typically utilized in creating the DSSS spreading and data waveforms and enables the creation of fundamentally miniature radio transmitters for use in embedded telemetry systems and the like. This reduction in complexity and size enables extremely small, battery-operated telemetry solutions such as are being deployed in location-based services devices.
2. Description of the Related Art
Direct sequence spread spectrum radio transmission is a method utilized in the art for communicating wireless voice and data. Advantages of using DSSS as the radio modulation means include security, fade resistance, low probability of intercept, and multiple use of channel spectrum. This modulation means was first conceived in 1941 by Hollywood actress. Hedy Lamarr and pianist George Anthiel, who obtained U.S. Pat. No. 2,292,387 entitled “Secret Communication System.” DSSS use was largely constrained to secure voice and data communication systems until the late 1980s, when the Federal Communications Commission allocated several frequency spectrum bands for unlicensed, multi-user purposes. DSSS was a logical choice for radio modulation due to the ability for multiple users to simultaneously use the spectrum and the associated receiver to differentiate the desired transmitter. Commercial utilization of DSSS modulation became widespread, with DSSS techniques utilized in terrestrial WiFi links, wireless alarm systems such as described in U.S. Pat. Nos. 4,977,577 and 5,987,058 entitled “Wireless Alarm System” to Sanderford et al., commercial satellite television systems such as Direct TV, and commercial satellite communication systems such as the Globalstar Simplex Data Service. These systems all share the common modulation method whereby the data is mixed with a broadband random or pseudo-random signal, thereby creating a broadband modulated data signal to be radio-transmitted. The system receiver recovers the data by mixing the broadband transmitted signal with the identical and in-phase randomization signal. The art of creating and receiving. DSSS signals is well known.
DSSS as a modulation data method is inherently more complicated than analog systems such as amplitude modulation (AM) or frequency modulation (FM). Creation and mixing of the broadband randomization signal requires hardware and software methods and means that are not required for simpler modulation methods. Implementing the system components of transmitters and receivers requires a level of complexity that has been the focus of technology development since DSSS inception. Designers have two options—develop custom application-specific integrated circuits (ASIC) or use commercially available hardware and software systems to construct the DSSS components. ASIC development is costly but can result in fundamentally miniaturized hardware solutions. A strong business case is typically required to make the investment for custom circuitry such as ASICs. WiFi is an example of a DSSS system that has passed the consumer volume thresholds that enable ASIC development. On the other extreme are low-volume terrestrial point-to-point data links that are generally specific to an application. Designers wishing to develop DSSS links for lower-volume applications often use off-the-shelf commercial components for cost reasons, but these off-the-shelf components increase the overall size of the device.
Designers continue to scour commercial product offerings to find new and better ways to construct system components. In particular, the expanding communications capabilities in hand-held telephones fuels new chipsets that can be used to develop spin-off communication systems. The present invention utilizes a combination of components that were developed for different applications and that, when combined as taught herein, significantly narrow the gap between full ASIC and commercial off-the-shelf DSSS transmitter capability. The present invention utilizes two commercially available chips to create a DSSS transmitter functionality that overcomes existing barriers in size, power (energy) requirements, and cost.
The first chip used in the present invention is a microprocessor component that incorporates a programmable logic capability, which provides the ability to create software-plus-hardware functionality in a single chip. The manufacturer of this chip calls it a programmable system on a chip (PSoC), and it is commercially offered in a large variety of configurations. The first generation of the PSoC family is called PSoC1 and was fueled in production volume by sales of the Apple iPod. The PSoC family of mixed signal arrays is manufactured by Cypress Semiconductor Corporation (“Cypress”) of San Jose, Calif. and has grown to include two subsequent PSoC families.
The second chip is a radio frequency (RF) I/Q modulator. The I/Q modulator is one of several chips being driven in volume by cellular telephone demand. It merges together frequency synthesis and data modulation and, in some cases, amplification into one chip. Two examples of such a chip are the ADRF6702 manufactured by Analog Devices, Inc. of Wilmington, Mass., and the RFMD2081 manufactured by RF Micro Devices, Inc. of New Delhi, India. The term “I/Q” is a term used in the telecommunications industry to refer to the in-phase (“I”) and quadrature (“Q”).
The present invention is a system and method for incorporating a DSSS modulation capability in the smallest of the PSoC1 devices, utilizing the least capable programmable logic functionality offered by the manufacturer. In a preferred embodiment, the present invention performs this function in a commercial component that measures 3×3 mm, in a 16 pin PSoC1 part, available at a cost of approximately $1 USD. Present state-of-the-art for developing a DSSS baseband modulator is provided by Cypress in the application note AN2165. In contrast to what is taught in the application note, the present invention performs this functionality utilizing only half of the required PSoC resources. The reduction in required PSoC resources represents the fundamental innovation of the present invention and results in DSSS transmitter development that achieves embedded circuit layout space under 0.75″×0.5″ and, in one embodiment, a mere 0.5″×0.5″ square footprint.
The present invention is directly applicable to satellite communication systems and specifically suited for use in the Globalstar Simplex Data Service. The latter service utilizes one-way, transmit-only terrestrial devices that incorporate a DSSS transmitter to collect data globally through DSSS receive-only gateway earth stations. Current state-of-the-art Globalstar DSSS transmitters utilizing commercial off-the-shelf components are nine to 12 times larger. The present invention teaches how to utilize the resources of the PSoC1 mixed signal array coupled with now available I/Q modulators to achieve an overall size reduction that enables battery-operable mobile devices to operate in smaller and more power-efficient applications that could never before be served. For example, the present invention can radio-enable a remote battery-powered sensor that is roughly the size of a single AA battery, compared to the existing sensor devices that typically are 3″×6″ in size or larger.
This reduction in size enables the sensor monitoring and asset tracking of package-sized assets versus the larger devices, which are limited in application to tracking larger assets, such as the trucking and railcar-tracking solutions offered today. For example, size reduction of RFID chips has enabled use of the devices in animal identification as well as small package tracking. Similarly, reduction of size in satellite tracking tags will open markets for small parcel tracking and tracking of small animals such as birds and marine wildlife.
Accordingly, it is an object of the present invention to provide a method for implementing a DSSS baseband modulator in a PSoC1 mixed signal processor suitable as a component of a DSSS transmitter. It is a further object of the present invention to provide a method for constructing the DSSS transmitter utilizing the PSoC1 and an I/Q modulator.